Ideally, a tire is desirable to be a perfect circle, and interior stiffness, dimensions and weight distribution and other features thereof should be uniform around the circumference of the tire. However, the usual tire construction and manufacturing process make it difficult to mass produce such an ideal tire. That is, a certain amount of nonuniformity in the stiffness, dimensions and weight distribution and other features occur in the produced tire. As a result, an undesirable exciting force is produced in the tire while the vehicle is running. The oscillations produced by this exciting force are transmitted to the vehicle chassis and cause a variety of vehicle oscillations and noises including shaking, fluttering, and sounds of the tire vibrations being transmitted inside the vehicle.
Industry standards are available for evaluating nonuniformity of a tire. In one method, a rotating drum, which serves as a substitute for the road surface, presses against a rotatably held tire with a predetermined pressing force (several hundred kilograms), or the tire is pressed against the rotating drum with the predetermined pressing force. The tire and the rotating drum are capable of rotating around their respective rotational axes, in such a way that when either one rotates, the other is also caused to rotate.
In this condition, the tire or the rotating drum is rotatably driven so that the tire rotates at 60 revolutions per minute. As the tire rotates, the exciting force produced by nonuniformity of the tire occurs. This exciting force is measured by one or more force measuring devices (such as a load cell) mounted on a bearing which rotatably supports the tire or the rotating drum, or mounted on a member attached to this bearing. From the measured value, an index that serves to evaluate the nonuniformity of the tire is computed. This measurement is referred to as a uniformity measurement.
Tires on which measurements were performed are classified into those for which the nonuniformity obtained from the index is within tolerable limits and those for which it is not. To the extent possible, tires for which the nonuniformity is outside of the tolerable limits are subjected to processing to decrease the nonuniformity. Tires that have been processed are then subjected to uniformity measurement again; those for which the nonuniformity is within tolerable limits are separated from those for which it is not.
Through the procedure described above, only tires judged to have “nonuniformity within tolerable limits” are selected and shipped to customers (or sent to the next step in the tire evaluation procedure).
Although current tire uniformity machines are believed to be effective, it is believed that further improvements can be obtained. Current tire uniformity machines provide test results that are sometimes inconsistent. In determining whether a uniformity machine is reliable, a same tire will be tested five times to ensure that the machine consistently detects and measures any nonuniformities in the tire. An additional sampling of tires are also then subjected to the same uniformity tests. From this collection of test results, various filters can be generated and applied to production tires to filter actual results. As skilled artisans will appreciate, filtering the test results undesirably adds time to the test procedure. Filtering also raises concerns that the filters may be set to exclude tires that are acceptable and, more problematically, tires that are not acceptable may be passed to allowance. Therefore, there remains a need to accurately and quickly test a tire. As such, there is a need to characterize components of a tire uniformity machine so that those characterizations can be filtered out of the test results so as to more accurately and quickly pass tires to allowance that are acceptable and reject tires that are not acceptable.